Question

A spinning ice skater will speed up if he brings his arms close to his body. Which of the following statements explains this phenomenon?
A. Angular momentum is always conserved.
B.A centripetal force always points outward.
C. Circular motion is always uniform.
D.Centripetal acceleration cannot change.

Answer 1

A. Angular momentum is always conserved would be the correct answer.

This is because like linear momentum (mvmv), angular momentum (r×mvr×mv) is a conserved quantity, where rr is the vector from the center of rotation. For a skater holding a static pose, for each particle making up her body, the contribution in magnitude to the total angular momentum is given by mirivimirivi. Thus bringing in her arms reduces riri for those particles. In order to conserve angular momentum, there is then an increase in the angular velocity.

hope this helps!

Answer 2

Answer:

A. Angular momentum is always conserved.

Explanation:

When ice skater is spinning then during skating the ice skater have no external torque on his body.

So here we can say

$\tau = \frac{dL}{dt}$

net torque on a system is rate of change in angular momentum

so here we will have

$0 = \frac{dL}{dt}$

so we can say

$L = constant$

so if ice skater bring his arm closed then his angular momentum will remains conserved during this motion